Finishing plaster
The finishing plaster is the top of a two- or multi-layer mortar layer, consisting of a base plaster and a finishing plaster, which is applied to the masonry in separate work steps. It primarily serves to protect against external mechanical influences, such as precipitation (driving rain) and in the color design of the facade or the interior walls.
The two-layer structure of the base and top plaster has historical causes and is still recommended today by experts, although the plaster manufacturers are very happy to deny that it is necessary. The background is that the wall structure from the masonry (previously almost exclusively fired bricks) to the surface has to equalize the different expansion behavior so that the entire plaster structure is able to flexibly absorb both the thermal and static stresses of the masonry. In addition, the surface should have the necessary flexibility and hardness as protection. The wall structure to the outside is therefore: hard (masonry) - soft (concealed) - hard (upper plaster).
Nowadays, the finishing plaster for the outside area is already colored at the factory, which is a significant cost factor with a construction of at least two layers, based on the amount that is required to be colored: The concealed plaster, and that is the larger amount, does not need this coloring.
Finishing plaster exterior plaster
The type of finishing plaster to be used depends on the continuous load the plaster has to withstand. Exterior plasters are exposed to wind, frost and strong temperature fluctuations and must withstand these influences. They should retain their color for many years, continue to adhere well and remain crack-free. The mineral exterior plasters - characterized by their binding agents, air lime, hydraulic and highly hydraulic lime, lime-cement mixtures and cement - meet these requirements when they are cured. They have been used for hundreds of years. The aggregates here are different sands or fine gravel, which also determine the surface structure and thus the effectiveness of the function of the outer protective shell of the building.
The modern synthetic resin exterior plasters are ready-made mixes that are characterized primarily by their efficient processing. If used correctly, their surface is largely free of cracks, only at the beginning more elastic than lime plasters, more weather-resistant, more abrasion-resistant and also more water-repellent. Due to their polymer content, diffusion is delayed in the first 1–2 years of service life, but not completely prevented, which is why the prejudice that one has a plastic film around the building is correct. As a rule, it should be noted that it is difficult for water to penetrate this plaster surface, but conversely that which has penetrated diffuses just as slowly. Therefore, capillary-open systems such as air-lime mortar are highly recommended for brick construction.
Plaster types based on gypsum or anhydrite are unsuitable as finishing plaster outdoors, as they absorb water (as rain and also humidity) like a sponge. This changes their strength, so that there is no longer any surface protection.
In the case of the thermal insulation composite system (ETICS), the connection between the base and surface plaster must be supported by a primer, since normal plaster cannot absorb the physically induced stresses of the ETICS without this connection aid.
Finishing plaster interior plaster
In contrast to the external plaster, the interior plaster should be predominantly level and also smooth. In order to regulate the room climate, they must be permeable to water vapor, capillary suction and provide a suitable substrate for painting and wall and ceiling wallpaper. The historically grown interior plaster is the mortar plaster , which consists of various limes and sand. For interior plasters, however, significantly less cement is added, or in some cases no cement , as this reduces the good diffusion properties of the plaster. In the interior, the special form of the binder is anhydrite binder instead of lime. Gypsum plaster, which can be designed to be particularly smooth, is predominantly used for machine interior plasters that are common today. Occasionally used light and fine plasters especially for indoor use are offered ready-mixed, whereby these have a lower surface hardness than their counterparts for outdoor use.
For the same reasons, which is why they are not used outside, gypsum plasters are also unsuitable in damp rooms.
See also
literature
- Klaus-Jürgen Schneider (Ed.), Georg Sahner (Ed.): Masonry Construction Current - Practical Guide 2007 . Bauwerk, Berlin 2006, ISBN 3-89932-152-9 .
- Klaus-Jürgen Schneider and Michael Zinnman: Building knowledge database . (Electronic Resource). Bauwerk-Verlag, Berlin 2005, ISBN 3-89932-116-2 .
- Helmut Weber: Facade protection and building renovation - The guide for the renovation, conservation and restoration of buildings . (Contact + Study Series, Volume 40: Building Practice). expert-verlag, Renningen-Malmsheim 1994, ISBN 3-8169-0690-7 .